This invention relates to a structure of a multi-tube evaporator, especially to a structure of a capillary arranged between a refrigerant supply header and each of the evaporating tubes of a multi-tube evaporator for a cooler used in an automobile.
In a cooling system of a cooler used in an automobile, gaseous refrigerant is discharged from a compressor at high pressure and fed into a condenser. The gaseous refrigerant is condensed into liquid refrigerant in the condenser. The liquid refrigerant is forced to pass through the expansion means of refrigerant and fed into an evaporator. The pressure of the liquid refrigerant is reduced by the capillary. While the liquid refrigerant changes into the gaseous refrigerant in the evaporating tubes of the evaporator, the refrigerant takes evaporation heat away from the surroundings of the evaporator. The gaseous refrigerant is discharged from the evaporator and is back to the compressor.
In such a cooling system, it is desirable to attain an uniform distribution of the liquid refrigerant throughout the whole evaporating tubes of the evaporator. The uniform distribution of the liquid refrigerant causes highly efficient operation of the evaporator.
U.S. Pat. No. 2,707,868 discloses that capillaries had previously been unsuccessfully in an attempt to produce equal distribution of refrigerent to each of a plurality of evaporator tubes and teaches the use of metering orifices disposed at each entrance for the liquid refrigerant into the evaporating tubes. The refrigerant is fed to the orifices or restrictions at relatively high pressure. The flow of the refrigerant into the respective tubes is accurately governed and uniform distribution of the refrigerant is attained. However, U.S. Pat. No. 2,707,868 does not disclose the specific structure of the unsuccessful capillaries.
The diameter of a capillary depends upon the dimensions of the evaporating tubes, and the dimensions of the evaporating tubes depend upon the load of the evaporator. For example, if the evaporating tube has 6.8 millimeters in its diameter and has 1.8 meters in its length, then the capillary is desirable to have about 1 millimeter in its diameter and have 80 to 130 millimeters in its length. The use of a fine tube as a capillary is proposed in a U.S. patent application Ser. No. 692,760 ("COMPRESSION TYPE REFRIGERATION APPARATUS FOR AUTOMOBILES" in the name of Kawashima et al., filed on June 4, 1976 abandoned). However, the fine tube has following defects. (1) A spiral fine tube used as a capillary is difficult to manufacture. (2) One end of the spiral capillary tube opens in the evaporating tube and the other end opens in the refrigerant supply header in which all evaporating tubes open. The spiral capillary tube is supported at each end thereof by the refrigerant supply header and the evaporating tube respectively. As a result, the spiral capillary tube has a small resistance against the vibration of the evaporator.